Why are life expectancy and obesity going up in tandem?
#1: More people are exercising than they used to. How many joggers and walkers did you see on the streets 20, 30 years ago?
#2: Fewer people are smoking. Forget lung cancer (if you can). The big risk for smokers is premature vascular disease. Normally we all have carbon monoxide in our blood (it comes from the breakdown of hemoglobin). [ Brit. Med. J. vol. 296 pp. 78 - 79 '88 ] Natural carbon monoxide production would lead to a carboxyhemoglobin level of .4 - .7%, but normal levels in nonsmokers in urban areas are 1 - 2%. Cigarette smoke contains 4% carbon monoxide, so smokers have levels of 5 - 6%. This can't be good for their blood vessels.
#3: Doctors know more than they did. My brother is a very competent internist. He took over the practice of a similarly competent internist after his very untimely many death years ago. Naturally he got all the medical records on the patients. He found letters (now over 25 years old) from the late MD to his patients informing them of their lab results, and assuring them that their cholesterol was just fine at 250 mg%.
#4: The drugs are better. In addition they may be working in ways that we have yet to fathom. Consider the statins -- their effect on vascular disease is far greater than their effect on blood lipids (cholesterol, triglyerides) -- particularly when compared to other agents that lower blood lipids to the same extent.
#1 can't be it, since most obese people probably don't jog. I would imagine the second is very powerful--and also somewhat related to quitting smoking, since the average weight gain after quitting is six to eight pounds, and one in ten smokers appears to gain up to thirty pounds. Smoking is much, much worse for your health than being fat. I imagine #3 and #4 contribute as well.
(H/t Derek Lowe)